As far as I remember the Switch doesn't actually use uPnP. The only thing that I had to do to achieve NAT Type B was an outgoing NAT with static port enabled. If I understood right, NAT Type A can only be achieved if your device literally had a WAN address.
Holy shit they are actually suggesting to put their console in DMZ??? https://en-americas-support.nintendo.com/app/answers/detail/a_id/22272 https://en-americas-support.nintendo.com/app/answers/detail/a_id/22489
There was nobody in the company that said "but wait"?
If someone has more than a console per household needs to get another internet connection in order to online play?
Networking isn't their strong suite, lol
Yeah, that's just basically every unregistered UDP port... Not much you can do about it since Nintendo has struggled to understand the internet and its uses since the Famicom.
And no, for the love of God don't enable uPnP. It's still pretty much the worst thing you can do.
I put my Nintendo Switch into a DMZ/own vlan. It was simpler and so I can get a NAT type A on it.
Just get a steam deck instead
The real answer